1. Field of the Invention
The present invention relates to an ionization method for a substance and a mass spectrometry method using the ionization method. The present invention also relates to an extraction method and purification method for a substance.
2. Description of the Related Art
A mass spectrometry method that is one of component analysis methods involves ionizing components in a sample and measuring and analyzing the mass-to-charge ratio (mass number/charge number) thereof.
In recent years, techniques of creating an image of the distribution of components existing on a solid sample surface are developed. The distribution of a particular component is visualized as a mass image, whereby conditions of a sample can be determined. As an example of such techniques, a method of showing data that serves as the basis for a pathological diagnosis, based on a mass image of a pathological specimen including cancer tissue is developed. A mass image is generally acquired by: ionizing a sample at a plurality of measurement points; obtaining the mass-to-charge ratio of the generated ions for each measurement point; and associating a position on the sample surface with ion information. Hence, in order to improve the spatial resolution of the obtained analysis result, a technique of ionizing a micro region on the sample surface is required.
Patrick J. Roach et al., “Nanospray desorption electrospray ionization: an ambient method for liquid extraction surface sampling in mass spectrometry” Analyst, 135, pp 2233-2236 (2010) proposes a method of: imparting a solvent to a micro region on a solid sample surface such that components existing in the micro region are dissolved; and ionizing the dissolved components under an atmosphere pressure. This method uses: a first capillary configured to provide the solvent for dissolving the components in the solid sample, to the sample surface; and a second capillary configured to move a mixture solution in which the components are dissolved in the solvent, to an ionization site. In the state where the two capillaries are close to the solid sample surface, the solvent is provided thereto by the first capillary, whereby a liquid bridge is formed between the leading ends of the two capillaries and the sample surface. In the liquid bridge, only a contact portion of the solid sample is dissolved, and the dissolved portion is then introduced to the second capillary. A high voltage is applied to the solvent, and ionization is performed at the leading end of the second capillary. This method enables the ionization of the micro region. Further, because the ionization is performed under an atmosphere pressure, the time required for measurement can be shortened, and the size of an apparatus can be reduced. Hence, this method is advantageous when a large number of samples are analyzed.
International Publication No. WO 2011/060369 proposes a method of: irradiating a mixture solution containing a sample dissolved therein, with a surface acoustic wave; and thus ionizing the contained components under an atmosphere pressure. According to this method, the mixture solution in which the sample is dissolved in a solvent is placed on a substrate, and is irradiated with the surface acoustic wave, thus achieving liquid atomization and then sample ionization. Moreover, according to International Publication No. WO 2011/060369, the ionization efficiency can be improved by applying voltage to the mixture solution.
A technique of detecting biological components as multiply charged ions is also required in mass spectrometry for materials of biological origin such as biological tissue. In the case where the molecular weight of a detection target component is relatively large, if the mass-to-charge ratio is made lower by imparting many electric charges, the component can be easily detected by even a detector whose detectable mass-to-charge ratio is low.